British light-heavyweight Joshua Buatsi earned a win yet disappointing start to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a split decision in a close ten-round contest at the Manchester venue.
But Parker landed significant shots, delivering effective single shots in a match where the styles failed to mesh, with frequent clinching spoiling the action.
Two judges scored it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my best performance but what defines champions? They prevail," the victor commented in the ringside as he was greeted with disapproval from the audience.
The Londoner bounced back after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Several boxing experts felt Parker, thirty-one, should have been awarded the decision but the contender experienced the second defeat of his 28-fight career.
Buatsi Secures Triumph in Uneventful Encounter
Buatsi's progress has slowed in the past few years through contract problems and long spells of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now stands trying to realize his potential - perhaps in what feels like a last chance - under fresh management.
He started carefully, with the two boxers ready to take risks in a tentative opening few rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after damaging his hand in the contest, was participating in his second appearance at the higher weight class.
By the halfway stage, the underdog had stayed in contention, making life awkward for the favorite, who operated with a protective stance to narrowly win the cleaner periods.
The audience's tolerance wore thin during frequent holding, with the challenger slipping to the canvas several times during grappling.
The underdog ended stronger, but multiple periods were difficult to score. However, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
The victor moves on, but with the caliber of power puncher Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Hatton Homage Inspires Manchester Derby Fight
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a outstanding all-Manchester contest to capture the European light heavyweight championship.
The stadium fell silent for a profoundly moving memorial prior to the bout as ten bells sounded in memory of the city's native Ricky Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast match card in the location since Hatton's passing. As the last bell faded, the silence transitioned to a chant of "only one Hatton".
The action during the bout matched the feeling. The eventual winner was sent to the canvas by a left hook directly to the face in the early round, getting up unsteadily to his footing on the eight count.
But the red-colored shorts of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was injured early, significant bruising developing under his eye as the duo exchanged punishing blows.
Rea, 27, delivered effective strikes but Arthur, 34, responded in kind with effective uppercuts as the action rarely dropped over the full distance.
The victor edged the result with official scores of draw, 115-113 and 115-112, but each competitor were persistent and brave, exactly what their idol Hatton represented.
